Ce travail de thèse a consisté à étudier la nature chimique, les origines, ainsi que les propriétés des aérosols en Afrique de l’Ouest. Nous avons en particulier recherché les liens entre la composition chimique des particules fines en surface et les propriétés optiques des aérosols. Notre étude s’est appuyée sur les mesures effectuées au cours de la campagne de terrain SHADOW sur le site de M’Bour (Sénégal) durant deux périodes d’observations intensives : mars à juin 2015 (POI-1) et novembre 2015 à janvier 2016 (POI-2). Un dispositif instrumental permettant une caractérisation chimique en ligne et à haute résolution temporelle des aérosols submicroniques (TEOM-FDMS, ACSM, aéthalomètre) a été mis en place, en parallèle d’instruments de mesure des propriétés optiques des aérosols en surface (aéthalomètre, néphélomètre) et sur la colonne atmosphérique par télédétection (photomètre, Lidar). Les données météorologiques couplées à différents outils statistiques ont permis de classer les espèces ayant une contribution locale et/ou régionale, et d’identifier les zones sources à l’origine des fortes concentrations. La modélisation sources-récepteur (PMF) a permis une analyse approfondie de la fraction organique des PM1, mettant en évidence une photochimie très active et l’influence d’activités anthropiques spécifiques (incinération de déchets, fumage de poisson). Nous avons pu caractériser, selon la saison, les types d’aérosols contribuant majoritairement à l’extinction des particules fines mesurée en surface à M’Bour, ainsi que mettre en évidence les liens/différences entre mesures de télédétection et propriétés chimiques/optiques des particules fines au cours des deux POI. / The aim of this thesis consists in studying the chemical nature, the origins as well as the optical properties of aerosols in West Africa. We focused on establishing the links between the chemical composition of fine particles at surface and aerosols optical properties. Our study is based on measurements acquired during the SHADOW field campaign, implemented on the M’Bour (Senegal) site during two intensive observation periods: March to June 2015 (IOP-1) and November 2015 to January 2016 (IOP-2). For this purpose, an instrumentation allowing online chemical characterization of surface PM1 (ACSM, TEOM-FDMS, aethalometer), at high time resolution, was implemented in parallel with instruments measuring aerosols optical properties at surface (aethalometer, nephelometer) and along the atmospheric column by remote sensing (Lidar, photometer). The coupling of meteorological data with statistical tools allowed determining the local and/or regional contribution of the different species, and identifying the source areas responsible for the high concentrations observed on site. The source receptor model (PM) allowed to further investigate the submicronic organic fraction, highlighting a fast photochemistry and the influence of specific anthropogenic activities (waste burning, fish smoking). We were also able to characterize, per season, the type of aerosols contributing to the fine particle extinction measured at surface, as well as to show links/differences between remote sensing and surface chemical/optical properties of fines particles during the two IOP.

Ce travail de thèse expérimental traite de la caractérisation et de l'optimisation de sources d'électrons et de photons (gamme en énergie keV- MeV) produites lors de l'interaction d'un laser à impulsion courte et intense avec une cible à l'état de plasma. La caractérisation en énergie et angulaire de ces sources est un enjeu d'importance, notamment dans la perspective de les utiliser pour des expériences de physiques nucléaires dans les plasmas. Une partie de ce travail est consacrée à l'étude des écrans photostimulables (IPs), détecteurs couramment utilisés pour la mesure des distributions en énergie et angulaire des faisceaux de particules accélérées par laser. Les caractéristiques des écrans de type MS, SR et TR de la marque Fuji ont été étudiés et leurs fonctions de réponse aux électrons, photons, protons et particules alpha sont établies dans une gamme en énergie de quelques kev à plusieurs MeV. Enfin un protocole est proposé pour réaliser des mesures quantitatives avec ces détecteurs dans différentes configurations expérimentales.Dans une seconde partie, une source d'électrons produite avec l'installation ELFIE du LULI dans la gamme en énergie de l'ordre du MeV a été caractérisée et optimisée en faisant varier l’extension spatiale du pré-plasma dans lequel interagi le laser intense. En particulier nous montrons que plus de 1011 électrons de plus de 10 MeV sont accélérés lors de l’interaction laser- plasma pour des conditions particulières d’extension longitudinale du pré-plasma en amont, mais aussi en aval de la cible.Dans une dernière partie, une source de photons produite à haute cadence avec le laser AURORE du CELIA est étudiée dans une gamme en énergie d'une dizaine de keV. L’originalité de la source réside dans la nature de la cible qui est du gallium à l'état liquide. Nous montrons en particulier que l'énergie moyenne et le nombre des photons peuvent être optimisés en créant des jets de gallium à la surface de la cible au moyen d'une pré-impulsion laser. Une interprétation physique du phénomène est proposée s’appuyant sur des simulations numériques. / This work takes place in the framework of the characterization and theoptimization of laser-driven electron and photon sources. With the goal of usingthese sources for nuclear physics experiments, we focused on 2 energy ranges:one around a few MeV and the other around a few tens of keV. The first partof this work is thus dedicated to the study of detectors routinely used forthe characterization of laser-driven particle sources: Imaging Plates. A modelhas been developed and is fitted to experimental data. Response functions toelectrons, photons, protons and alpha particles are established for SR, MS andTR Fuji Imaging Plates for energies ranging from a few keV to several MeV. Thesecond part of this work present a study of ultrashort and intense electron andphoton sources produced in the interaction of a laser with a solid or liquid target.An experiment was conducted at the ELFIE facility at LULI where beams ofelectrons and photons were accelerated up to several MeV. Energy and angulardistributions of the electron and photons beams were characterized. The sourceswere optimized by varying the spatial extension of the plasma at both the frontand the back end of the initial target position. In the optimal configuration ofthe laser-plasma coupling, more than 10exponent11 electrons were accelerated. In the caseof liquid target, a photon source was produced at a high repetition rate on anenergy range of tens of keV by the interaction of the AURORE Laser at CELIA(10exponent16 W cm exponent-2) and a melted gallium target. It was shown that both the meanenergy and the photon number can be increased by creating gallium jets at thesurface of the liquid target with a pre-pulse. A physical interpretation supportedby numerical simulations is proposed.

En physique de l’atmosphère, la reconstruction d’une source polluante à partir des mesures de capteurs est une question importante. Elle permet en effet d’affiner les paramètres des modèles de dispersion servant à prévoir la propagation d’un panache de polluant, et donne aussi des informations aux primo-intervenants chargés d’assurer la sécurité des populations. Plusieurs méthodes existent pour estimer les paramètres de la source, mais leur application est coûteuse à cause de la complexité des modèles de dispersion. Toutefois, cette complexité est souvent nécessaire, surtout lorsqu’il s’agit de traiter des cas urbains où la présence d’obstacles et la météorologie instationnaire imposent un niveau de précision important. Il est aussi vital de tenir compte des différents facteurs d’incertitude, sur les observations et les estimations. Les travaux menés dans le cadre de cette thèse ont pour objectif de développer une méthodologie basée sur l’inférence bayésienne adaptative couplée aux méthodes de Monte Carlo pour résoudre le problème d’estimation du terme source. Pour cela, nous exposons d’abord le contexte scientifique du problème et établissons un état de l’art. Nous détaillons ensuite les formulations utilisées dans le cadre bayésien, plus particulièrement pour les algorithmes d’échantillonnage d’importance adaptatifs. Le troisième chapitre présente une application de l’algorithme AMIS dans un cadre expérimental, afin d’exposer la chaîne de calcul utilisée pour l’estimation de la source. Enfin, le quatrième chapitre se concentre sur une amélioration du traitement des calculs de dispersion, entraînant un gain important de temps de calcul à la fois en milieu rural et urbain. / In atmospheric physics, reconstructing a pollution source is a challenging but important question : it provides better input parameters to dispersion models, and gives useful information to first-responder teams in case of an accidental toxic release.Various methods already exist, but using them requires an important amount of computational resources, especially as the accuracy of the dispersion model increases. A minimal degree of precision for these models remains necessary, particularly in urban scenarios where the presence of obstacles and the unstationary meteorology have to be taken into account. One has also to account for all factors of uncertainty, from the observations and for the estimation. The topic of this thesis is the construction of a source term estimation method based on adaptive Bayesian inference and Monte Carlo methods. First, we describe the context of the problem and the existing methods. Next, we go into more details on the Bayesian formulation, focusing on adaptive importance sampling methods, especially on the AMIS algorithm. The third chapter presents an application of the AMIS to an experimental case study, and illustrates the mechanisms behind the estimation process that provides the source parameters’ posterior density. Finally, the fourth chapter underlines an improvement of how the dispersion computations can be processed, thus allowing a considerable gain in computation time, and giving room for using a more complex dispersion model on both rural and urban use cases.

Three pen trials were conducted to evaluate the value of A. saligna as a source of feed for ruminants. In Trial 1 A. saligna was inadequate as the sole source of nutrients for sheep. Furthermore, the level of detannification achieved in Trial 1, with the addition of PEG 4000 or PEG 6000, failed to improve the diet sufficiently. The antinutritional effects on the animals were largely attributed to the excessive biological activity of the phenolics in the A. saligna leaves. Feeding of these leaves, without PEG, had a definite defaunating effect on the ruminal fluid. The ruminal ammonia levels were all well below the threshold for maximal microbial growth. Given the results of Trial 1, the second trial was undertaken to determine if A. saligna was more useful as a supplement rather than a basal diet. The benefits of including A. saligna as a supplement to a basal diet of lupins and wheat straw were not clear. The benefits of including a detannification agent with the A. saligna were also not evident. Ruminal ammonia levels were much higher than in Trial 1 and animals generally maintained weight. Trial 2 revealed that the sheep were capable of consuming significantly more A. saligna than they did in Trial 1, but it was not clear whether this was due to the basal diet providing adequate nutrients or if it was due to differences in the A. saligna fed in the respective trials. Total phenolics, CT and PPC were considerably lower than those of Trial 1. Trial 3 was designed to investigate the use of A. saligna as the basal source of nutrients, with or without a supplement of N in the form of urea or PEG. Total phenolics, CT and PPC were lower than those of Trial 1, but higher than those of Trial 2. Animals consumed more A. saligna than in Trial 2 and generally maintained weight. / The results from Trial 3 suggest that A. saligna could be a useful feed source for ruminants. The substitution of straw with A. saligna indicates that its incorporation into a grazing system could significantly decrease grazing pressure on dry summer pastures. In Trial 3 goats were not shown to have a superior ability than sheep in utilising A. saligna as a source of nutrients.

Business today is faced with discontinuity and unpredictable change, which makes many of the structured processes of yesteryear redundant or obsolete. Process-based transactions are being replaced with technology and increasingly organisations are recognising the importance of proactively managing their knowledge transactions, to remain competitive. While research on knowledge sharing is gaining the attention of researchers, almost invariably their focus has been on the factors influencing knowledge transfer at the macro-level in large multi-national organisations. Few have attempted to unravel the complexities of individual-to-individual micro-level knowledge sharing and those that have, for the most part have directed their investigations towards exploring factors that enhance or impede the source individual sharing their knowledge, rather than the recipient's receiving of knowledge. While questioning is implicit in knowledge sharing there are assumptions that underpin the structure of a question and these assumptions affect both the source and the recipient. This study investigates how the structure of a question posed to a source individual when eliciting knowledge, influences the attitude of a recipient individual towards the knowledge they receive from the question response. Drawing upon theoretical assumptions that underpin question structure, three hypotheses are posed to compare binary, open-ended and directed question responses. To test the hypotheses a progression of three independent studies were performed using laboratory and field experiments. The first study conducted in a laboratory, used a contrived scenario case as the knowledge context and the second study replicated this experiment in the field. The last study conducted in a single organisation, used real organisational knowledge as the knowledge context. Recipients of shared knowledge were found to be more favourably disposed towards question responses that were structured in a complex manner; open-ended and directed question responses were more favoured than binary question responses. ii There was no difference in recipient attitude between open-ended and directed question responses and recipient attitude towards the shared knowledge was found to be positively related to their intention to use the knowledge in the future. These findings are of significance as they illustrate the importance of structuring questions in a manner that is consistent with recipients of the shared knowledge being more favourably disposed towards the knowledge they have received. In an environment of ambiguity, complexity and uncertainty where decisions are nonprogrammed, strategic and imperative to the competitiveness of the organisation, no longer is the binary 'Yes' or 'No' compliance or audit style question, with its implicit assumptions, sufficient to elicit knowledge. It is important to recognise that often we do not know what we need to know until it is shared by someone. Further, when shared knowledge is cognitively processed with our current knowledge base, the new knowledge is likely to facilitate more informed decision-making. The more favourably disposed the recipient is towards the knowledge the more likely it is that they will use it in the future; knowledge is transferred.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (viewed Feb. 8, 2007). PDF text: 140 p. : ill. (some col.) ; 0.72Mb. UMI publication number: AAT 3216341. Includes bibliographical references. Also available in microfilm and microfiche format.

Tanning bed use, especially among young, white females, has become a serious health problem in the United States. Those who use tanning beds value a tanned appearance; thus, one possible way to get individuals to stop using tanning beds is to persuade them to begin using an alternative method: a sunless tanner. This study sought to use persuasive messages to encourage individuals to both stop using tanning beds and start using a sunless tanner. Deviance Regulation Theory (DRT) was used to design three messages, and source expertise was manipulated (high and low). In addition, attitudes, perceived norms, benefits and threats about tanning were examined. Results indicate that the combination of DRT message design and source expertise produced several message conditions that were effective at decreasing tanning bed use intent. No combined message condition was effective at changing sunless tanner use intent. DRT message design alone did not produce results, nor did source expertise. Tanning attitudes were influenced by reference groups, and perceived norms about tanning predicted individual‘s tanning bed use for several reference groups. In addition, there was an interaction between benefits and threats of tanning.

This essay is an ideographic study over the capacity of high school students to use the Internet with source criticism, and their attitudes towards this media. It’s a qualitative study whose main purpose is to seek out how the students reflect upon the problems facing them when searching facts and information over the internet.The focus group is six 18 year old high school students, who are studying in a normal sized town in the middle of Sweden, and are about to finish their studies in the program for social sciences. The study was made through interviews, one on one with the students,The results of the analysis have shown that even if students not necessarily use a pre meditated method when searching for information over the internet, they do have a basic understanding of the matter, especially concerning the nature of the source, who published it and why. Not all students made any thorough comparison with other, already established media, such as TV or books, but the analysis made it clear that they more or less deliberately saw the established media as more trustworthy in general. Individuals publishing on the internet, such as bloggers and Wikipedia, are seen with the utmost skepticism while public institutions such as universities and public service TV, are generally trusted as being honest and objective, also when publishing on the internet.

Tanning bed use, especially among young, white females, has become a serious health problem in the United States. Those who use tanning beds value a tanned appearance; thus, one possible way to get individuals to stop using tanning beds is to persuade them to begin using an alternative method: a sunless tanner. This study sought to use persuasive messages to encourage individuals to both stop using tanning beds and start using a sunless tanner. Deviance Regulation Theory (DRT) was used to design three messages, and source expertise was manipulated (high and low). In addition, attitudes, perceived norms, benefits and threats about tanning were examined. Results indicate that the combination of DRT message design and source expertise produced several message conditions that were effective at decreasing tanning bed use intent. No combined message condition was effective at changing sunless tanner use intent. DRT message design alone did not produce results, nor did source expertise. Tanning attitudes were influenced by reference groups, and perceived norms about tanning predicted individual‘s tanning bed use for several reference groups. In addition, there was an interaction between benefits and threats of tanning.

Controlled source electromagnetic (CSEM) geophysics has been used with a fair amount of success in near surface hydrogeological studies. Recently, these investigations have been conducted frequently in human impacted field sites containing cultural conductors such as metal fences and buried pipes. Cultural noise adds an element of complexity to the geological interpretation of this type of data. This research investigates the influence of mutual induction between two buried targets in a CSEM experiment. In particular, it looks at the mutual coupling between a buried cultural conductor and a geological heterogeneity. We attempt to isolate the Hz field induced by tertiary currents in targets caused by mutual coupling. This is achieved with a Texas A&M 3D CSEM finite element code, which calculates the secondary Hz fields emanating from a target buried in a halfspace. Buried geological targets and cultural conductors are modeled as volumetric slabs embedded in a halfspace. A series of models have been simulated to study the effect of varying parameters such as target conductivity, transmitter location and shape of a target on the mutual inductance. In each case, the secondary Hz field is calculated for a model with two slabs, and two models with individual slabs. The mutual coupling is calculated by removing the secondary fields from the individual slab models from the response of a two slab model. The calculations of mutual inductance from a variety of such models suggests a complicated interaction of EM fields between the two targets. However, we can explain most of these complexities by adapting a simple approach to Maxwell’s equations. Although the tertiary Hz field is complicated, it may be useful in the characterization and delineation of electrical heterogeneities in the subsurface, which can then be related to geological features such as fractures or joints. It is seen that the most important factor affecting the mutual coupling is the host conductivity. The results have also shown that mutual coupling is very sensitive to transmitter (TX) location, especially when the TX is positioned near one of the targets.